JP2016531961A - Separation of salt by-products during the formation of polyarylene sulfide. - Google Patents

Abstract

A method of forming polyarylene sulfide and a system that can be used in the practice of this method are described. The forming method includes a filtration process to treat the mixture comprising polyarylene sulfide, salt by-products of the polyarylene sulfide forming reaction, and a solvent. The filtration process involves maintaining the downstream side of the filter media at an elevated pressure. The downstream pressure can allow the boiling point of the mixture at the downstream pressure to be higher than the temperature at which the polyarylene sulfide is insoluble in the solvent. [Selection] Figure 1

Description

  [0001] This application is filed in US Provisional Patent Application 61 / 882,332 having a filing date of 25 September 2013; and US Provisional Patent Application 62 / 033,289 having a filing date of 5 August 2014; (Both of which are hereby incorporated by reference in their entirety) claim the filing date benefits.

  [0002] Polyarylene sulfides are high performance polymers that can withstand high thermal, chemical, and mechanical stresses and are beneficially used in a wide range of applications. Polyarylene sulfides are generally formed by polymerizing dihaloaromatic compounds with alkali metal sulfides or alkali metal hydrosulfides in organic amide solvents. Salts are formed as by-products in the polymerization reaction, and these salt by-products must be removed to obtain a final product that exhibits the desired properties.

  [0003] Standard methods for removing salt byproducts include the use of screens or sieves due to particle size differences between polyarylene sulfide and salt byproducts. Unfortunately, these methods are ideal for loss of product in the form of polyarylene sulfide particulates and undesirable levels of salt by-products that remain trapped in the product polyarylene sulfide granules. It turns out that it is not. Water extraction is used for the purpose of removing residual salts after filtration / sieving operation, which brings additional steps and associated costs to the forming process, and polyarylene sulfide during filtration / sieving operation The problem of fine particle loss is not solved.

  [0004] Solid / liquid extraction processes have also been used to remove salt by-products from the polymerization product. The extraction method is quite effective, but requires a large amount of water, thus generating both waste and additional operating costs. Other separation processes are used, such as sieving and / or water extraction after flushing the solvent, but these methods, like others, cost, additional process steps, and undesirable waste Bring into the forming process.

  [0005] There is a need in the art for a method of removing salt byproducts during the formation of polyarylene sulfide polymers that can keep capital costs low and avoid further waste formation.

  [0006] A method of forming a polyarylene sulfide polymer is disclosed. For example, the method can include reacting a dihaloaromatic compound with an alkali metal sulfide or alkali metal hydrosulfide in an organic amide solvent to form a polyarylene sulfide polymer and salt. The mixture comprising polyarylene sulfide, salt, and organic amide solvent can then be subjected to a filtration process. In the filtration process, the mixture flows from the upstream to the filter media and the filtrate flows downstream from the filter media while the salt is retained in the filter media to form a salt cake. The pressure downstream of the filtration process may be higher than atmospheric pressure, and the boiling point of the mixture at the downstream pressure may be higher than the lowest temperature at which the polyarylene sulfide is completely soluble in the solvent. Thus, the downstream pressure functions to keep the polymer in solution during filtration, and the filtration is below the boiling point of the mixture at the downstream pressure and below the lowest temperature at which the polyarylene sulfide is completely soluble in the solvent. Can also be carried out in a high temperature range.

  [0007] In one embodiment, the reaction may be a first stage polymerization reaction of a multi-stage polyarylene sulfide formation process, and the polyarylene sulfide may be of a relatively low molecular weight upon filtration. In this embodiment, the process can also include a second stage polymerization reaction stage during which the molecular weight of the polyarylene sulfide can be increased.

  [0008] The present invention may be better understood with reference to the following drawings.

[0009] FIG. 1 is a flow diagram for a polyarylene sulfide formation process including a salt byproduct separation process described herein. [0010] FIG. 2 shows the filter media after performing a salt by-product separation process using a pressure downstream of atmospheric pressure during filtration. [0011] FIG. 3 is a salt by-product that maintains the downstream pressure such that the boiling point of the filtrate at the downstream pressure is higher than the temperature at which the polyarylene sulfide polymer is completely soluble in the solvent. Fig. 4 shows the filter media after performing the separation process.

  [0011] It will be appreciated by those skilled in the art that this discussion is a description of representative aspects only and is not intended to limit the broader forms of the invention.

  [0012] The present invention relates generally to a method of forming polyarylene sulfide and systems that can be used in the practice of this method. More specifically, a filtration process is disclosed for treating a mixture comprising polyarylene sulfide, a salt byproduct of a polyarylene sulfide forming reaction, and a solvent. The filtration process involves maintaining an elevated pressure downstream of the filter media. The downstream pressure can be such that the boiling point of the mixture at the downstream pressure can be higher than the lowest temperature at which the polyarylene sulfide is completely soluble in the solvent. Filtration can be performed within a temperature range between the boiling point of the mixture and the temperature at which the polymer is completely soluble in the solvent. Thus, the downstream pressure functions to maintain the polymer in solution during filtration.

  [0013] During the filtration process, the pressure differential across the filter media may be static or may vary during the process. In either case, the pressure differential across the filter media can be controlled to ensure that the filtration process can proceed at a reasonable rate. This filtration process allows the removal of salt by-products from the mixture according to a simple, fast and reliable method that can use existing filter technology with lower capital costs. In addition, the method can use less solvent in the final wash of the polyarylene sulfide, thereby reducing the waste generated during the polyarylene sulfide formation process.

  [0014] By using this filtration process, most or all of the salt by-products formed during the polymerization reaction can be removed with little or no precipitation of polyarylene sulfide in the filtration unit. it can. Thus, the filtration process reduces or eliminates waste production because it can reduce or eliminate longer filter life, less production interruption time, and extraction operations that produce waste that was required in the past. Can bring. Furthermore, the present method can eliminate the need for a sieving process due to dimensional differences between the polyarylene sulfide granules and the salt by-products.

  [0015] According to one aspect, the filtration process can be used to increase the molecular weight of the polyarylene sulfide during the polymerization reaction during which the polyarylene sulfide formed therebetween is a relatively low molecular weight prepolymer. Can be carried out prior to the second stage polymerization reaction to reach a useful value. By separating the salt by-product prior to the second stage polymerization reaction, a lower solvent / sulfur ratio can be used in the second stage, thus increasing the reaction rate of the second stage reaction and increasing the polymer concentration and Further improvements in the forming process can be realized, such as effectively increasing the forming rate. In addition, by performing a salt separation process prior to the second stage polymerization reaction, the volume of the reactor for the second stage can be increased because salt is removed from the mixture charged to the second stage reactor. .

  [0016] However, this is not an essential requirement of the filtration process; in other embodiments, the filtration process can be performed after a polymerization reaction in which the polyarylene sulfide formed therebetween is a high molecular weight polymer. For example, the filtration process can be performed after a single polymerization process or after a second (or subsequent) polymerization stage in a multi-stage polymerization process.

  [0017] The formation process to produce the polyarylene sulfide includes reacting a compound that provides a hydrosulfide ion, such as an alkali metal sulfide or alkali metal hydrosulfide, with a dihaloaromatic compound in an organic amide solvent. be able to. One embodiment for forming polyarylene sulfide is shown in FIG. According to this aspect, the first stage polymerization reaction in which the monomer is reacted in the first stage to form a polyarylene sulfide prepolymer having a relatively low molecular weight can be performed.

  [0018] In general, the polyarylene sulfides that can be formed according to the present methods have the formula (I):

(Wherein Ar ¹ , Ar ² , Ar ³ , and Ar ⁴ are the same or different and are arylene units of 6 to 18 carbon atoms; W, X, Y, and Z are the same or different. , —SO ₂ —, —S—, —SO—, —CO—, —O—, —COO—, or a divalent linking group selected from an alkylene or alkylidene group of 1 to 6 carbon atoms. , At least one of the linking groups is -S-; and n, m, i, j, k, l, o, and p are independently 0, or 1, 2, 3, or 4. Yes, but the sum of these is 2 or more)
The polyarylene thioether containing the repeating unit of The arylene units Ar ¹ , Ar ² , Ar ³ , and Ar ⁴ may be optionally substituted or unsubstituted. Preferred arylene systems are phenylene, biphenylene, naphthylene, anthracene, and phenanthrene. The polyarylene sulfide may contain more than about 30 mol%, more than about 50 mol%, or more than about 70 mol% of arylene sulfide (—AR—S—) units. In one aspect, the polyarylene sulfide comprises at least about 85 mol% of sulfide linking groups that are directly bonded to two aromatic rings.

[0019] In one aspect, the polyarylene sulfide formed by the present method, phenylene sulfide structure as the component in the present invention _{:-( C 6 H 4 -S) n} - ( wherein, n an integer of 1 or more The polyphenylene sulfide is defined as including.

  [0020] Monomers used in the formation of polyarylene sulfides can include alkali metal sulfides, which can be, for example, lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, cesium sulfide, or mixtures thereof. If the alkali metal sulfide is a hydrate or an aqueous mixture, the alkali metal sulfide can be treated by a dehydration operation prior to the polymerization reaction. Alkali metal sulfides can also be generated in situ. In addition, a small amount of alkali metal hydroxide may be included in the reaction to remove impurities such as alkali metal polysulfide or alkali metal thiosulfate that may be present in very small amounts with the alkali metal sulfide, or It can be reacted (eg, changing such impurities into harmless materials).

  [0021] The dihaloaromatic compound can be charged to the first stage polymerization reaction along with the alkali metal sulfide. Dihaloaromatic monomers include, without limitation, o-dihalobenzene, m-dihalobenzene, p-dihalobenzene, dihalotoluene, dihalonaphthalene, methoxy-dihalobenzene, dihalobiphenyl, dihalobenzoic acid, dihalodiphenyl ether, dihalodiphenylsulfone, dihalo It may be halodiphenyl sulfoxide or dihalodiphenyl ketone. The dihaloaromatic compounds can be used either alone or in any combination thereof. Specific representative dihaloaromatic compounds include, without limitation, p-dichlorobenzene; m-dichlorobenzene; o-dichlorobenzene; 2,5-dichlorotoluene; 1,4-dibromobenzene; 1,4-dichloro 1-methoxy-2,5-dichlorobenzene; 4,4'-dichlorobiphenyl; 3,5-dichlorobenzoic acid; 4,4'-dichlorodiphenyl ether; 4,4'-dichlorodiphenyl sulfone; -Dichlorodiphenyl sulfoxide; and 4,4'-dichlorodiphenyl ketone.

  [0022] The halogen atom of the dihaloaromatic compound may be fluorine, chlorine, bromine, or iodine, and the two halogen atoms in the same dihaloaromatic compound may be the same or different from each other. In one embodiment, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, or a mixture of two or more of these is used as the dihaloaromatic compound.

  [0023] As known in the art, a monohalo compound (not necessarily (It is not an aromatic compound).

  [0024] The polyarylene sulfide may be a homopolymer or a copolymer. Polyarylene sulfide copolymers containing two or more different units can be formed by a suitable selective combination of a plurality of dihaloaromatic monomers. For example, when p-dichlorobenzene is used in combination with m-dichlorobenzene or 4,4'-dichlorodiphenylsulfone, the formula (II):

A segment having the structure of formula (III):

A segment having the structure: or formula (IV):

A polyarylene sulfide copolymer containing segments having the following structure can be formed.

  [0025] Generally, the amount of one or more dihaloaromatic compounds per mole of effective amount of alkali metal sulfide to fill is 1.0-2.0 moles, 1.05-2.0 moles, or 1 .1 to 1.7 moles. Thus, the polyarylene sulfide may contain alkyl halide (eg, alkyl chloride) end groups.

[0026] In other embodiments, a copolymer can be formed and has the formula (V):

Wherein the groups R ¹ and R ² are independently of one another a hydrogen, fluorine, chlorine or bromine atom, or a branched or unbranched alkyl or alkoxy group having 1 to 6 carbon atoms.
The monomer can be charged to the system. In one aspect, the monomer of formula (V) may be p-hydroxybenzoic acid or one of its derivatives.

  [0027] Other monomers that can be charged to the system are those of formula (VI):

It may have the structure. One example of a monomer of formula (VI) is 2-hydroxynaphthalene-6-carboxylic acid. Both monomers of Formula V and VI can be loaded into the system to form a polyarylene sulfide copolymer.

  [0028] The polyarylene sulfide copolymer has the formula (VII):

(Wherein Ar is an aromatic group or more than one condensed aromatic group and q is a number from 2 to 100, in particular from 5 to 20)
And a segment derived from the polyarylene sulfide structure. The group Ar in formula (VII) may be a phenylene or naphthylene group. In one aspect, the second segment can be derived from poly (m-thiophenylene), poly (o-thiophenylene), or poly (p-thiophenylene).

  [0029] The polyarylene sulfide may be linear, semi-linear, branched, or crosslinked. Linear polyarylene sulfide contains a repeating unit of-(Ar-S)-as a main structural unit. In general, the linear polyarylene sulfide may contain about 80 mol% or more of this repeating unit. The linear polyarylene sulfide may contain a small amount of branching or crosslinking units, but the amount of branching or crosslinking units may be less than about 1 mol% of the total monomer units of the polyarylene sulfide. The linear polyarylene sulfide polymer may be a random copolymer or block copolymer containing the above-mentioned repeating units.

[0030] A semi-linear polyarylene sulfide can be formed, which is a crosslinked structure or branch provided by introducing a small amount of one or more monomers having three or more reactive functional groups into the polymer. It may have a structure. For example, between about 1 mol% and about 10 mol% of the polymer can be formed from monomers having three or more reactive functional groups. Methods that can be used in the production of semi-linear polyarylene sulfides are generally known in the art. As an example, the monomer component used in the formation of the semi-linear polyarylene sulfide can include a predetermined amount of a polyhaloaromatic compound having two or more halogen substituents per molecule that can be used in the production of the branched polymer. Such monomers have the formula: R′X _n , wherein each X is selected from chlorine, bromine, and iodine, n is an integer from 3 to 6, and R ′ is about 4 or less methyl substituted A polyvalent aromatic group of valence n which may have a group, the total number of carbon atoms in R ′ being in the range of 6 to about 16. Examples of some polyhaloaromatic compounds substituted with more than two halogens per molecule that can be used in the formation of the semi-linear starting polyarylene sulfide include 1,2,3-trichlorobenzene, 1,2, , 4-trichlorobenzene, 1,3-dichloro-5-bromobenzene, 1,2,4-triiodobenzene, 1,2,3,5-tetrabromobenzene, hexachlorobenzene, 1,3,5-trichloro- 2,4,6-trimethylbenzene, 2,2 ′, 4,4′-tetrachlorobiphenyl, 2,2 ′, 5,5′-tetraiodobiphenyl, 2,2 ′, 6,6′-tetrabromo-3 , 3 ′, 5,5′-tetramethylbiphenyl, 1,2,3,4-tetrachloronaphthalene, 1,2,4-tribromo-6-methylnaphthalene, and the like, and mixtures thereof And the like.

  [0031] Representative organic amide solvents used in the formation of polyarylene sulfides include, without limitation, N-methyl-2-pyrrolidone; N-ethyl-2-pyrrolidone; N, N-dimethylformamide; N, N- Mention may be made of dimethylacetamide; N-methylcaprolactam; tetramethylurea; dimethylimidazolidinone; hexamethylphosphoric triamide, and mixtures thereof. The amount of organic amide solvent used in the reaction may be, for example, 0.2-5 kilograms (kg / mol) per mole of effective amount of alkali metal sulfide.

[0032] During the initial stages of polymerization, a complex comprising an alkali metal organic amine and an alkali metal hydrogen sulfide is obtained by mixing a predetermined amount of an organic amide solvent with an alkali metal sulfide, an alkali metal hydroxide, and water. Can be formed. For example, sodium methylaminobutyrate (SMAB) and sodium hydrogen sulfide (NaSH) can be formed by mixing a predetermined amount of alkali sulfide salt, N-methylpyrrolidone (NMP), water, and sodium hydroxide to form a mixture. Can be formed. The mixture can be subjected to heating until the temperature of the mixture reaches about 200 ° C to about 210 ° C. During this reaction, a combination of water, NMP, and some H ₂ S can be recovered as distillate. The distillate can be analyzed, for example, by chromatography to determine the composition of the mixture during the first stage of polymerization.

[0033] When carrying out this stage of the polymerization reaction, usually an alkali metal sulfide containing water can be charged into the organic amide solvent, and the mixture is heated to distill off excess water from the reaction system. be able to. At this point, part of the alkali metal sulfide decomposes to form alkali and hydrogen sulfide (H ₂ S). The effective amount of the filled alkali metal sulfide can be calculated from the amount of H ₂ S produced.

  [0034] The completion of this initial stage of the polymerization reaction during which the complex is formed generally indicates that the conversion rate of the dihaloaromatic compound in the reaction system is about 50 mol% or more of the theoretical conversion rate, about 70 mol%. It is the time when the above or about 90 mol% or more is reached. The theoretical conversion of the dihaloaromatic compound can be calculated from one of the following formulas.

  (A) When the dihaloaromatic compound is added in excess (by molar ratio) over the alkali metal sulfide,

  (B) In cases other than (a)

  Where X is the amount of dihaloaromatic monomer charged; Y is the residual amount of dihaloaromatic monomer; Z is the excess (mole) of dihaloaromatic monomer.

(C) In cases other than (a) or (b)
Conversion rate = A / B × 100
Where A is the total weight of salt recovered after removal of other species other than residual polymer and salt by-products; B is the theoretical weight of salt (the molar amount of effective sulfide present during polymerization). 2 times).

  [0035] After the complex is formed, the mixture comprising the complex is reacted with a dihaloaromatic monomer at a temperature of, for example, about 180 ° C to about 280 ° C, or about 200 ° C to about 260 ° C, to form a low molecular weight A prepolymer can be formed. This initial polymerization can be continued until the conversion of the dihaloaromatic compound reaches about 50 mol% or more of the theoretical required amount.

[0036] After this polymerization reaction, the average molar mass of the prepolymer represented by weight average molecular weight: _Mw is from about 500 g / mole to about 30,000 g / mole, from about 1000 g / mole to about 20,000 g / mole. Mole, or about 2000 g / mol to about 15,000 g / mol.

  [0037] The polymerization reaction apparatus is not particularly limited, but it is usually desirable to use an apparatus that is usually used in forming a high viscosity fluid. Examples of such a reactor include an anchor type, a multistage type, a spiral ribbon type, a screw shaft type, etc., or a stirring tank type polymerization reaction having a stirring device having various shapes of stirring blades such as these deformed shapes. An apparatus can be mentioned. Further examples of such a reaction apparatus include a mixing apparatus usually used in kneading such as a kneader, a roll mill, a Banbury mixer and the like.

  [0038] After the polymerization reaction is performed to form a low molecular weight prepolymer, the mixture may include a prepolymer, a solvent, and one or more salts. For example, the molar ratio of solvent to sulfide can be from about 1 to about 10, or from about 2 to about 5. The ratio of the salt formed as a byproduct to the reaction (by volume) may be from about 0.05 to about 0.25, or from about 0.1 to about 0.2.

  [0039] Salts included in the reaction mixture may include those formed as by-products during the reaction and other salts added to the reaction mixture, for example, as a reaction accelerator. The salt may be organic or inorganic, i.e. composed of any combination of organic or inorganic cations and organic or inorganic anions. These may be at least partially insoluble in the reaction medium and may have a density different from that of the liquid reaction mixture. Typical examples of inorganic salts are alkali or alkaline earth metal halides that may be formed as a by-product of one or more polymerization reactions. Representative examples of organic salts include carboxylates of organic substituted ammonium cations that can be used as promoters in the production of alkali metals, alkaline earth metals, ammonium, or polyarylene sulfides. As used herein, carboxylate refers to solids of aliphatic carboxylic acids, such as acetic acid or propionic acid, or aromatic carboxylic acids, such as benzoic acid, as well as polyfunctional carboxylic acids.

  [0040] For mixtures having a solids content between about 20 wt% and about 30 wt% typical of the formation of polyarylene sulfide prepolymers, polyarylene sulfide at atmospheric pressure and temperatures from about 220 ° C to about 230 ° C Often precipitates. The boiling point of the solvent can vary, but it is often in the range of about 200 ° C to about 220 ° C. For example, the boiling point of N-methyl-2-pyrrolidone is about 202 ° C. at atmospheric pressure. If the conditions are such that the boiling point of the mixture is below the lowest temperature at which the polyarylene sulfide is completely soluble in the solvent, polymer precipitation occurs at a temperature between these two temperatures. there is a possibility. This can occur with any solvent-containing mixture that includes the polymer. However, the boiling point of the mixture increases at elevated pressure. Thus, in the hot filtration process described herein, the pressure during the filtration process (ie, both upstream and downstream of the filter) rises above atmospheric pressure, and the filtration process is the minimum pressure of the filtration process (eg, Downstream pressure) and at a temperature below the boiling point of the mixture at a temperature above the minimum temperature at which the polymer is completely soluble in the solvent. The difference between the boiling point of the mixture at the lowest pressure of the filtration process and the lowest temperature at which the polymer is completely soluble in the solvent can provide a temperature range in which the filtration process can be performed. For example, the difference between these two temperatures may be about 10 ° C. or higher in some embodiments, or about 15 ° C. or higher in some embodiments, eg, about 10 ° C. to about 50 ° C. in some embodiments. It may be.

  [0041] Referring to FIG. 1, the filtration process can include a filtration unit 100, where the pressure downstream of the filter media 110 (eg, the outlet shown in FIG. 1) is such that the boiling point of the mixture at this downstream pressure is Such that the polyarylene sulfide is above the lowest temperature at which it is completely soluble in the solvent. For example, the downstream pressure may be greater than about 300 kilopascals (kPa). In some embodiments, the downstream pressure may be about 300 kPa to about 1200 kPa, about 400 kPa to about 1100 kPa, or about 500 kPa to about 1000 kPa.

  [0042] In addition to the increased downstream pressure, the filtration process maintains a positive pressure differential across the filter media 110 to provide a desired flow rate across the filter media 110 and an efficient filtration process. It can be carried out. For example, the pressure differential across the filter media 110 (eg, from inlet to outlet as shown in FIG. 1) is about 30 kPa to about 500 kPa, about 50 kPa to about 400 kPa, or about 70 kPa during at least a portion of the filtration process. It may be ~ 300kPa.

  [0043] The mixture and filtrate can be heated throughout the filtration process to prevent precipitation of the polyarylene sulfide. For example, the mixture and filtrate can be at a temperature of about 220 ° C to about 300 ° C. Further, the mixture and filtrate can be at the same temperature or different from each other. Furthermore, to ensure that the elevated temperature of the material is maintained and to avoid undesired precipitation of polyarylene sulfide at any point in the filter unit (ie, the entire unit 100 as well as on the filter media 110). The filter unit 100 can be heated to or near the temperature of the mixture and / or filtrate. For example, at least the portion of the filter unit 100 that contacts the mixture and filtrate can be maintained at a temperature between about 220 ° C and about 300 ° C.

  [0044] The pressure upstream and downstream and the pressure difference between the two can be kept constant or can be varied throughout the filtration process as long as the two basic criteria are met. These two criteria are (1) the downstream pressure is the lowest pressure of the filtration process (ie the boiling point of the mixture at this downstream pressure is higher than the lowest temperature at which the polyarylene sulfide is completely soluble in the solvent) Pressure); and (2) the upstream pressure is higher than the downstream pressure. Several representative embodiments of static and dynamic pressure systems that meet these basic criteria are described below.

  [0045] According to one aspect, the pressure differential across the filter media 110 can be kept constant during the filtration process to maintain a constant positive pressure during the filtration process. For example, the constant pressure differential across the filter media 110 can be between about 50 kPa and about 400 kPa. In one aspect, the upstream pressure can be maintained at about 800 kPa throughout the filtration process, the downstream pressure can be maintained at about 550 kPa, and a constant pressure differential of about 250 kPa is maintained throughout the filtration. can do.

  [0046] In one aspect, the pressure differential across the filter media 110 can be maintained at a constant and maximum difference throughout the filtration process, and the upstream pressure is maximized so that the flow rate of the filtration process is maximized. And hold downstream pressure at a minimum. In general, the maximum allowable upstream pressure can be determined based on the filter media used, the constituent materials of the filter unit, and the pressurization capacity of the system. The lowest allowable downstream pressure is the lowest pressure possible at the operating temperature of the filtration process so that the operating temperature is between the boiling point of the mixture at the downstream pressure and the temperature at which the polymer is completely soluble in the solvent. Therefore, it can be determined.

[0047] The filtration process is not limited to those aspects that keep the upstream and downstream pressures constant during filtration, and the process can include dynamic upstream and / or downstream pressures. For example, the downstream pressure can be controlled to maintain a positive pressure differential across the filter media and avoid polymer precipitation, while both the upstream and downstream pressures are in the course of the filtration process. Can be lowered in between. According to one aspect, the pressure differential can be kept constant throughout the process, while the upstream pressure and the downstream pressure vary at a similar rate relative to each other. For example, the upstream and downstream pressures can be reduced at a linear and equivalent rate throughout the filtration process.
[0048] In a further aspect, after maintaining a constant pressure difference between the upstream pressure and the downstream pressure for a certain period of time, the filtration process maintains a constant pressure difference between the upstream pressure and the downstream pressure. Time varying can be included. For example, after maintaining a certain pressure difference for a certain time while decreasing both the upstream pressure and the downstream pressure at the same rate, the downstream pressure is the boiling point of the mixture at the downstream pressure, and the polyarylene sulfide is in the solvent. The lowest allowable downstream pressure can be reached that can be higher than the temperature at which it is completely soluble. At this point in the filtration process, the downstream pressure can be maintained at the lowest downstream pressure and the upstream pressure can continue to drop. The filtration process is then stopped when the upstream pressure drops and matches the downstream pressure.

  [0049] In yet another aspect, the upstream or downstream pressure can be maintained at a constant pressure throughout the process, and the downstream or upstream pressure can be correspondingly varied during the process. . For example, the downstream pressure can be held at the lowest downstream pressure throughout the filtration process, and the upstream pressure can be reduced at a linear rate from the highest allowable upstream pressure to the point where the upstream pressure matches the downstream pressure. At this point, the filtration process is stopped.

  [0050] The dynamic filtration process may in any way reduce the upstream and / or downstream pressure during all or part of the filtration process, or upstream during all or part of the process. It is not limited to either linearly changing the pressure and / or downstream pressure. For example, in one embodiment, the upstream pressure can be increased during the filtration process to prevent a decrease in flow rate that can be caused by the formation of filter cake on the filter media. Furthermore, the upstream pressure and / or the downstream pressure can be increased or decreased non-linearly, for example exponentially.

  [0051] In general, because both equipment and operating costs can increase with increased operating temperature and pressure, the pressure control design of the filtration process can be highly dependent on the costs involved. Thus, one desirable design may be at the lowest temperature and pressure that allows the filtration process to be carried out while avoiding polyarylene sulfide precipitation. However, other desirable designs can optimize flow rates with increased pressure and temperature. In one aspect, during the filtration process (eg, to maintain a desired pressure differential across the filter media) and / or during filter cake washing (to improve contact between the filter cake and the washing fluid). Additionally, the system can include a mechanical stirrer that can agitate the filter cake.

  [0052] Beneficially, the filtration units and filter media used in the filtration process can include standard materials commonly known in the art. For example, filter media, mesh screens, or sintered plates known in the art that are stable under filtration process conditions can be used. The mesh size or pore size of the filter media can be adjusted over a wide range and can be varied depending on the filtration process conditions, such as viscosity of the mixture, filter pressure, temperature, desired purity of the filtrate, and the like. The technical devices that can be used for the filtration process are known, for example, simple pressure filters, stirred pressure filters, trailing blade centrifuges, and rotating filters can be used, among others.

  [0053] After the filtration process, the filter cake can be washed to remove any liquid in the filtered mixture that may remain in the filter cake. This liquid may contain polyarylene sulfide in solution, which can be recovered by a washing process, thus increasing the polymer yield of the forming process. For example, the filter cake can be washed at a temperature at which the polymer is held in solution by the solvent found in the mixture. The resulting wash solution, which may contain diluted polymer, can be mixed with the filtrate of the filtration process. In one aspect, the filter cake can be agitated during washing to improve polymer recovery. The washed filter cake can be dried in one embodiment to recover the adhering solvent residue. The final filter cake can contain very little polyarylene sulfide. For example, the final dried filter cake can include less than about 1 wt% solvent, based on the weight of the filter cake, and less than about 1 wt% polyarylene sulfide, based on the weight of the filter cake.

  [0054] After washing, the salt cake can be removed from the filtration media and the filtration media can be reused. For example, the salt cake can be removed from the filter media by using a solids mouth in the system or by disassembling the filtration unit. The salt cake can be removed from the filtration by mechanical means (eg, a removal blade), by a pressure differential (eg, across the filter media, such as to blow the filter cake off the media), or by a combination of several methods. The salt cake can be removed in a dry or wet state as desired. For example, the solid salt cake can be stirred in a filtration unit and optionally mixed with a liquid, such as water, to form a slurry, which is then removed, for example, through a solids mouth in the system, It can be discarded in a suitable form, such as in a brine block.

  [0055] After the first and second stages of prepolymer formation and the filtration process, a third stage during which a polymerization reaction can be performed to increase the molecular weight of the polyarylene sulfide can be performed. During this polymerization step, water can be added to the filtrate such that the total amount of water in the polymerization system is less than about 2.5 moles per mole of effective alkali metal sulfide charged. Thereafter, the polymerization reaction mixture can be heated to a temperature of about 240 ° C. to about 290 ° C., about 255 ° C. to about 280 ° C., or about 260 ° C. to about 270 ° C., and the melt viscosity of the polymer thus formed. Polymerization can be continued until is increased to the desired final level. The elapsed time for this polymerization step may be, for example, from about 0.5 to about 20 hours, or from about 1 to about 10 hours. The weight average molecular weight of the polyarylene sulfide formed may vary as is known, but in one embodiment from about 1000 g / mol to about 500,000 g / mol, from about 2,000 g / mol to about 300,000 g. / Mol, or about 3,000 g / mol to about 100,000 g / mol.

  [0056] After this polymerization reaction, a second filtration process can be performed, whereby any further salts from the product mixture, such as any that are formed as the molecular weight of the prepolymer increases during the polymerization. Salt can be removed. Alternatively, the polymerization reaction can be followed by a filtration process, which can be the first filtration process of the system, i.e. a filtration process is also arranged between the first polymerization process and the second polymerization process. do not have to.

  [0057] After the final polymerization, the polyarylene sulfide can be solidified (if desired) and discharged from the reactor through an extrusion orifice, usually equipped with a die of the desired structure, cooled and recovered. Usually, the polyarylene sulfide can be discharged through a perforated die to form a strand, which is wound up in a water bath, pelletized and dried. The polyarylene sulfide may also be in the form of strands, granules, or powders.

  [0058] After polymerization, the polyarylene sulfide can be washed with a liquid medium. For example, the polyarylene sulfide can be washed with water, acetone, N-methyl-2-pyrrolidone, salt solution, and / or an acidic medium such as acetic acid or hydrochloric acid. The polyarylene sulfide can be washed in a sequential manner generally known to those skilled in the art. The polyarylene sulfide can be subjected to a hot water washing process. The temperature of the hot water wash may be about 100 ° C. or higher, for example, higher than about 120 ° C., higher than about 150 ° C., or higher than about 170 ° C. In general, distilled or deionized water can be used for hot water washing. In one aspect, hot water washing can be performed by adding a predetermined amount of polyarylene sulfide to a predetermined amount of water and heating the mixture under stirring in a pressure vessel. As an example, a bath ratio of about 200 g or less polyarylene sulfide per liter of water can be used. After the hot water wash, the polyarylene sulfide can be washed several times with warm water maintained at a temperature of about 10 ° C to about 100 ° C. Washing can be done in an inert atmosphere to avoid polymer degradation.

  [0059] To wash the polyarylene sulfide, an organic solvent that does not decompose the polyarylene sulfide can be used. Organic solvents include, but are not limited to, nitrogen-containing polar solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, 1,3-dimethylimidazolidinone, hexamethylphosphoramide, and piperazinone; dimethyl sulfoxide, dimethyl sulfone , And sulfolanes such as sulfolane; ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone, and acetophenone; ether solvents such as diethyl ether, dipropyl ether, dioxane, and tetrahydrofuran; chloroform, methylene chloride, dichloride Halogen-containing coals such as ethylene, trichloroethylene, perchloroethylene, monochloroethane, dichloroethane, tetrachloroethane, perchloroethane, and chlorobenzene Hydrogen solvents; alcohols and phenolic solvents such as methanol, ethanol, propanol, butanol, pentanol, ethylene glycol, propylene glycol, phenol, cresol, polyethylene glycol, and polypropylene glycol; and fragrances such as benzene, toluene, and xylene Group hydrocarbon solvents; Furthermore, the solvent can be used alone or as a mixture of two or more thereof.

  [0060] Washing with an organic solvent can be performed by immersing the polyarylene sulfide in the organic solvent and heating or stirring as necessary. The washing temperature for organic solvent washing is not particularly critical and the temperature may generally be from about 20 ° C to about 300 ° C. Although cleaning efficiency may increase with increasing cleaning temperature, generally satisfactory effects are obtained at cleaning temperatures of about 20 ° C. to about 150 ° C.

  [0061] In one aspect, organic solvent cleaning can be combined with hot water cleaning and / or hot water cleaning. When a high-boiling organic solvent such as N-methylpyrrolidone is used, the residual organic solvent can be removed by washing with water or warm water after washing with the organic solvent, and distilled water or deionized water can be used for this washing. Can be used for

  [0062] Polyarylene sulfides can be used to form products as are generally known in the art. For example, polyarylene sulfide can be used as a filler (for example, fibrous and / or particulate filler), coupling agent, impact modifier, antibacterial agent, pigment, lubricant, antioxidant, stabilizer, surfactant. , Waxes, glidants, solid solvents, and additives such as one or more of other materials added to improve properties and processability. Such optional materials can be used in conventional amounts in the mixture.

  [0063] The mixture that is melt processed to form the melt processed polyarylene sulfide composition includes from about 40% to about 90% by weight, for example, from about 45% to about 80% by weight of the mixture. A weight percent amount of polyarylene sulfide (or a blend of polyarylene sulfides) can be included.

  [0064] The polyarylene sulfide can be melt processed according to techniques known in the art. For example, polyarylene sulfide can be melt kneaded with one or more additives at a temperature of about 250 ° C. to about 320 ° C. in a single or multi-screw extruder. In one aspect, the polyarylene sulfide can be melt processed in an extruder that includes multiple temperature zones. For example, polyarylene sulfide can be melt processed in an extruder that includes a temperature zone maintained at a temperature between about 250 ° C and about 320 ° C.

  [0065] Conventional molding processes for forming articles comprising polyarylene sulfide can be used. For example, extrusion, injection molding, blow molding, thermoforming, foaming, compression molding, hot forging, fiber spinning and the like can be used.

  [0066] Molded articles comprising polyarylene sulfides that can be formed include, for example, structural and non-structural molded parts for electrical appliances, electrical materials, electronic products, fiber webs, and automotive engineering thermoplastic material assemblies. Can do. Typical automotive molded plastic parts are bonnet interior applications, such as fan covers, support members, wiring and cable jackets, covers, housings, battery trays, battery cases, ducts, electrical housings, fuses to name a few. Suitable for bath housings, blow molded containers, non-woven or woven geotextiles, baghouse filters, membranes, and pound liners. In addition to molded articles, extrudates, and fibers, other useful articles include electronic panels such as wall panels, overhead storage lockers, serving trays, seat backs, cabin partitions, window covers, and integrated circuit trays. System.

  [0067] Compositions comprising polyarylene sulfides can be used in a variety of electrical and electronic applications, including connectors and overmolded (insert molded) parts.

  [0068] Some aspects of the invention are provided solely by way of illustrating some embodiments and are not to be considered as limiting the scope of the invention or the manner in which it can be practiced. Indicates. Unless indicated otherwise, parts and percentages are given on a weight basis.

Example 1:
[0069] A 2 L titanium pressure reactor was charged with 443.7 g NMP, 20.3 g H ₂ O, and 84.9 g NaOH (96.4%). The reactor was sealed and heated to 100 ° C. To this mixture (SMAb-NaSH mixture) was added NaSH of 155.86g was melted (including 71.4% of NaSH and 0.7% of Na ₂ S). The reactor was heated to 205 ° C. and 75 mL of distillate containing water and NMP was collected.

  [0070] To this SMAB-NaSH mixture was added a preheated mixture (74 wt% solution) of paradichlorobenzene (p-DCB) in NMP. The reactor was sealed and the temperature was raised to 235 ° C. and held for 1 hour. The temperature was then raised to 245 ° C. and held for an additional 3 hours to form a prepolymer.

[0071] After the prepolymer was formed, the filtration process described herein was performed using a 1 L Mott filter to maintain the reactor at 350 kPa and remove salt byproducts. The filtration process was started at 235 ° C. The filtration rate was 3000 to 5000 L / m ² · h after the filter cake had accumulated to a height of about 300 mm. The filtrate was collected in a stirred pressure vessel heated to 240 ° C. to maintain the prepolymer in solution. The upstream side of the filter was maintained at 90 pounds per square inch gauge pressure (115 psia, 790 kPa) and 235 ° C., and the filtrate side was maintained at atmospheric pressure (no back pressure, 14.7 psia, 101 kPa) and about 200 ° C.

  [0072] The salt filter cake was washed three times with 300 g NMP preheated to at least 230 ° C. in a polymerization reactor. A washing filtrate rich in PPS was added to the first filtrate.

[0073] The filter cake was flushed with dry nitrogen to pre-dry sodium chloride. It was found that a residual moisture of less than 10% by weight could be achieved during 10-15 minutes of N ₂ flushing. This result was achieved only by injecting nitrogen from the pressure side to the filtrate side through the cake without using mechanical means to mix or move the filter cake. The obtained salt filter cake was a powdery and non-tacky product, and it was easy to handle solids. The sodium chloride particle size ranged from 20 to 60 microns. The filtrate containing the prepolymer was transferred into the polymerization reactor for further polymerization. Concentrate the filtrate to 20% solids using flash distillation at 235 ° C. to complete the polymerization by removing all unreacted pDCB, H ₂ O byproduct, excess NMP, and other volatiles. Staged. Subsequently, sulfide modifications were added (the melt viscosity of the polymer was increased from <1 poise to a final melt viscosity of 460 poise). The polymerization was carried out by heating the reactor to 245 ° C. and holding this temperature for 1 hour, then raising the temperature to 260 ° C. and holding it for 3 hours. After the hold time, 90 g of water was added through the pump and the reactor pressure was increased from 100 psi to 270 psi. After the addition, the temperature was cooled to obtain a granular PPS polymer. To isolate the PPS, the slurry was filtered and washed once with 1 L NMP, then 3 times acetic acid in 1 L water at 60 ° C., then 3 times water at 80 ° C. The washed polymer was dried in a vacuum oven at 104 ° C. The yield was 200 g (93% of theory).

  [0074] The filter media after filtration for this experiment is shown in FIG. In this sample, the downstream pressure (atmospheric pressure) corresponded to the boiling point for the filtrate below the temperature at which the polyphenylene sulfide is completely soluble in NMP. As a result, as can be seen in FIG. 2, polyphenylene sulfide precipitated and the filter was blocked.

Example 2:
[0075] The process of Example 1 was repeated, but in this example, the upstream side of the filter was held at 90 pounds per square inch gauge pressure (115 psia, 790 kPa) and 235 ° C, and the filtrate side was 65 pounds per square. Inch gauge pressure (80 psia, 550 kPa) and 235 ° C were maintained. The filtered filter media for this experiment is shown in FIG. In this sample, the downstream pressure corresponded to the boiling point for the filtrate above the temperature at which the polyphenylene sulfide is completely soluble in NMP. Thus, as can be seen in FIG. 3, there was no precipitation or filter clogging.

  [0076] While several representative aspects and details have been set forth for the purpose of illustrating the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention. It will be clear.

Claims (15)

A method of forming polyarylene sulfide, comprising:
Reacting a dihaloaromatic compound with an alkali metal sulfide or alkali metal hydrosulfide in an organic amide solvent to form a polyarylene sulfide and salt;
The mixture comprising the polyarylene sulfide, the salt, and the organic amide solvent is subjected to a filtration process, the mixture is allowed to flow from upstream of the filter media to the filter media, and the filtrate is allowed to flow downstream from the filter media and the filtration is performed. The salt is retained on the filter media during the process to form a filter cake, the filtration process having a downstream pressure, the downstream pressure being greater than atmospheric pressure, and the mixture at the downstream pressure. The boiling point is above the lowest temperature at which the polyarylene sulfide is completely soluble in the solvent, the filtration has an upstream pressure, and the upstream pressure is at least part of the filtration process, Higher than the downstream pressure, the filtration is lower than the boiling point of the mixture at the downstream pressure, and the minimum that the polyarylene sulfide is completely soluble in the solvent Carried out at a temperature range higher than degrees;
A method involving that.   2. The method of claim 1, further comprising heating the mixture and the filtrate during the filtration process, e.g., heating the mixture and the filtrate independently to a temperature of about 220 <0> C to about 300 <0> C. how to.   The method of claim 1, wherein the downstream pressure is greater than 300 kilopascals and / or the difference between the upstream pressure and the downstream pressure is at least part of the filtration process. A method that is between 30 kilopascals and about 500 kilopascals.   The method of claim 1, wherein the difference between the upstream pressure and the downstream pressure is constant during at least a portion of the filtration process, for example, the constant difference is about 50 kilopascals. To about 400 kilopascals and / or the constant difference is a maximum tolerance, or the upstream pressure is constant during the filtration process, and the downstream pressure is at least part of the filtration process A method wherein both the upstream pressure and the downstream pressure fluctuate during at least part of the filtration process.   The method of claim 1, wherein the difference between the upstream pressure and the downstream pressure varies during at least a portion of the filtration process, for example, one of the upstream pressure and the downstream pressure is the filtration process. A method in which both the upstream pressure and the downstream pressure fluctuate during the filtration process.   The method according to claim 1, wherein the alkali metal is sodium and / or the dihaloaromatic compound is dichlorobenzene, for example, dichlorobenzene is m-dichlorobenzene, o-dichlorobenzene, p- A process which is dichlorobenzene or a mixture thereof.   2. The method of claim 1, wherein the organic amide solvent is N-methylpyrrolidone and / or the polyarylene sulfide is a homopolymer or copolymer, for example, the polyarylene sulfide is linear.   The method of claim 1, wherein a low molecular weight prepolymer is formed by a polymerization reaction, for example, the polymerization reaction conversion rate of the dihaloaromatic compound is about 50% or more of the theoretical conversion rate, and / or the low A second polymerization wherein the weight average molecular weight of the molecular weight prepolymer is from about 500 grams / mole to about 30,000 grams / mole and the process is optionally performed either after or prior to the filtration process. Further comprising a reaction wherein the polyarylene sulfide after the second polymerization reaction has a weight average molecular weight of about 1,000 grams / mole to about 500,000 grams / mole, and optionally the second A method of performing a second filtration process after polymerization.   The method of claim 1, further comprising washing the filter cake after the filtration process, optionally mixing a washing solution from the washing step with the filtrate, the washing step optionally comprising the washing step. A method comprising agitating the filter cake. The method of claim 1, comprising:
Drying the filter cake;
Mixing the filter cake with a liquid to form a slurry;
The method further comprising one or more of removing the filter cake from the filter media and reusing the filter media.   2. The method of claim 1, further comprising mixing the polyarylene sulfide with one or more additives and / or shaping the polyarylene sulfide to form a product.   A system for carrying out the method according to claim 1, comprising a reactor and a filter unit, wherein the polyarylene sulfide is formed in the reactor and the filtration process is carried out in the filter unit. .   13. The system of claim 12, further comprising a second reactor downstream of the filter unit and / or a third reactor upstream of the filter unit.   13. The system according to claim 12, wherein at least a portion of the filter unit is heated.   15. The system according to claim 14, wherein at least the portion of the filter unit that contacts the mixture and the filtrate during the filtration process is heated.

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